Car tyre

ABSTRACT

A tyre having a tread is described. The tyre has a central portion located across an equatorial plane, a first shoulder portion located towards an outer side of the tyre and a second shoulder portion located towards an inner side of the tyre. The central portion is separated from the first shoulder portion by two first circumferential grooves. The first shoulder portion and the second shoulder portion have a plurality of first transverse grooves having a first end located substantially at the respective edge of the tread, having a width greater than or equal to about 4 mm and an axial extension equal to at least 50% of the width of the shoulder portion in which they are located.

The present invention relates to a car tyre, particularly to a high orultra high performance car tyre.

The car tyres have a tread provided with blocks delimited bycircumferential grooves extending in a substantially longitudinaldirection, and transverse grooves extending in a substantially axialdirection. The intersection of said grooves results in blocks shapedaccording to various, suitably conceived, shapes and arranged alongcircumferential rows placed side by side, each included between twosubsequent circumferential grooves.

The circumferential grooves may affect the directionality and stabilitycharacteristics of the tyre travelling with respect to the side (drift)thrusts directed parallel to the axis of rotation of the tyre.

The transverse grooves, in turn, may affect the traction characteristicsof the tyTe, i.e. its ability to transmit to the road surface thetangential thrusts parallel to the running direction, duringacceleration and braking phases.

When driving on a wet road surface, the circumferential and transversegrooves may also affect the water drainage in the contact patch(footprint area).

The Applicant has noticed that a number of transverse grooves having anaccentuated width improves the traction, especially on wet roadsurfaces, also providing a good flexibility of the blocks, but theoveruse thereof can endanger the performance on dry road surfaces andincrease the tyre noise, especially if the number of transverse grooveshaving an accentuated width is provided at the tyre shoulders. In fact,the ridges of the blocks and/or of the grooves continuously collides oneafter the other against the road surface thereby causing the most noise.

To be able to keep up a high safety standard under all circumstances,the tyre must have, in addition, excellent brake performances (both ondry and wet surfaces) as well as great aquaplaning resistance: twocharacteristics in conflict with each other because, to have a goodamount of tyre on the ground thereby improving the brake performance, alow void-to-rubber ratio is required, whereas to provide a good waterdrainage a suitable number and especially a proper width of the groovesare required (i.e. a high void-to-rubber ratio).

Further, a relatively high void-to-rubber ratio can increase the noiseand the wear of the tyre.

As regards the driveability, the Applicant noticed that vehicle masseshave to be balanced; generally, in order to improve the corneringstability and speed, the most recent cars, and particularly therear-wheel-drive sport cars, have a suspension system characterized atthe rear axle by the use of high camber angles.

Further, the Applicant noticed that such a characteristic affects theshape of the tyre footprint. FIG. 1 shows, by way of example, thefootprint or contact patch of a conventional tyre mounted on the leftfront wheel of a rear-wheel-drive vehicle. As it can be seen, duringtravelling in a straight stretch or when stationary, the footprint areahas a substantially trapezoidal or triangular shape tapering toward theouter side of the vehicle.

The Applicant noticed that sport cars, especially the rear-wheel-driveones, mounting tyres characterized by a footprint area similar to thatshown in FIG. 1, if subjected to sudden accelerations, can have the rearaxle oversteering or have a transitory zigzag motion caused by the lossof grip of the rear axle.

The Applicant believes that such a behavior is at least partly caused bythe fact that, if the tyres are subjected to sudden accelerations and/orduring cornering, being therefore subjected to high and/or sudden loadtransfer, the inner side of the tyre can undergo an excessive decreaseof the load and its outer side can undergo an excessive increase of theload resulting in an excessive and too sudden change in the tyrefootprint.

The Applicant realized that, in order to reduce or prevent the loss ofgrip during cornering resulting in sudden load transfers, the footprintarea have to be prevented from deforming up to concentrate almost solelyon the outer side of the tyre. The Applicant has therefore consideredproviding a tread pattern that, during cornering with sudden loadtransfer, allows the footprint area to be as much as possible graduallyand increasingly deformed towards a footprint shape at the mostsubstantially mirrored with respect to that in FIG. 1, that is longer onthe outer side of the tyre and tapered on the inner side (but withoutthe total loss of grip).

Furthermore, the tread pattern should have to guarantee goodtraction/braking performances both on wet surface and dry surfaces, lownoise and rolling resistance, wear evenness and wear resistance.

The Applicant found that a tread pattern able to solve the aboveexplained mutually conflicting problems comprises a low void-to-rubberratio in the central area and comprises shoulder portions having a lowerblock mobility on the shoulder portion facing the outer side of the carwith respect to the block mobility of the shoulder portion facing theinner side of the car.

An aspect of the present invention relates to a car tyre having a treadcomprising a central portion located across an equatorial plane, a firstshoulder portion located towards the outer side of the tyre and a secondshoulder portion located towards the inner side of the tyre.

The central portion is separated from the first shoulder portion by twofirst circumferential grooves.

The first shoulder portion and the second shoulder portion comprise aplurality of first transverse grooves having a first end locatedsubstantially at the respective edge of the tread, having a widthgreater than or equal to about 4 mm and an axial extension equal to atleast 50% of the width of the shoulder portion in which they arelocated.

The number of said first transverse grooves of the first shoulderportion is lower than the number of said first transverse grooves of thesecond shoulder portion.

The central portion comprises at least one circumferential ribcomprising a plurality of second transverse grooves.

The second transverse grooves have a maximum width smaller than or equalto about 3 mm and define, in said at least one circumferential rib, avoid-to-rubber ratio smaller than or equal to about 0.06, preferablysmaller than or equal to about 0.05.

The small void-to-rubber ratio of the rib or ribs of the centralportion, together with the small size of the transverse grooves, givethe tread band a high structural consistency in such an area, therebyproviding the tyre with excellent performances of driveability and quicktraction response. Furthermore, the high amount of tyre on the groundprovides for excellent brake performances on a dry road surface, as wellas low noise and low rolling resistance. The circumferential groovesprovide for good performances travelling on wet road surfaces.

At the same time, a different stiffness of the shoulder portions and, inparticular, the greater stiffness at the portion facing the outer sideof the tyre, counteracts an excessive deformability of such portions,and thus excessive change of the footprint area when the vehicle issubjected to sudden load transfers (in particular during cornering),such that, even in critical situations, at least part of the inner sideof the tread rests on the ground, thereby promoting the stability andsafety of the vehicle itself.

In the context of this description, the following definitions areadopted:

-   -   By “equatorial plane” of the tyre is meant a plane perpendicular        to the rotation axis of the tyre and dividing the tyre into two        symmetrically equal parts.    -   By “outer side of the tyre” is meant the tyre side facing the        outside of the vehicle on which the tyre is mounted.    -   By “inner side of the tyre” is meant the tyre side facing the        vehicle on which the tyre is mounted.    -   By “circumferential” or “longitudinal” direction is meant a        direction generally pointing to the direction in which the tyre        rotates or anyway slightly tilted with respect to the direction        in which the tyre rotates.    -   By “axial direction” or “axially” is meant a direction generally        parallel to, or anyway slightly tilted, with respect to the axis        of rotation of the tyre.    -   By “radial direction” or “radially” is meant a direction        substantially orthogonal to the axis of rotation of the tyre.    -   By “depth” of a groove is meant the depth of the groove measured        in a direction substantially orthogonal to the bottom of the        groove up to its radially outermost edges.    -   By “width” of a groove is meant the width detected with        reference to the width of the radially outer edges of the        groove.    -   By “void-to-rubber ratio” is meant the ratio between the total        area of the grooves of a determined portion of the tyre tread        pattern intended to rest on the ground (possibly of the whole        tread pattern) and the total area of the same portion of the        tread pattern (possibly of the whole tread pattern).    -   By axial extension of a groove or a portion thereof is meant the        length of its projection measured along an axial direction.    -   By inclination of a groove or a segment thereof is meant the        angle of the groove with respect to a direction parallel to the        equatorial plane of the tyre; for each groove portion, such an        angle refers to the angle (having an absolute value between 0°        and 90°) formed by a rotation from a direction parallel to the        equatorial plane up to the direction tangent to the groove        passing through such a portion.    -   By module of the tread pattern is meant a minimum portion of the        tread pattern repeated in succession and substantially unchanged        along the whole circumferential extension of the tread band        itself. Although modules keep the same pattern shape, they may        have different circumferential extensions.

In the above said aspect, the present invention may have at least one ofthe hereinafter described characteristics.

Preferably, for each module of the tread pattern the number of firsttransverse grooves of the second shoulder portion may be about twice thenumber of the first transverse grooves of the first shoulder portion.

Advantageously, the second transverse central grooves may have a firststraight segment extending over at least 50%, preferably at least 70%,of the total extension of the second transverse grooves. Preferably,said first substantially straight segment has an inclination α≥45°relative to the equatorial plane.

Conveniently, the first straight segment has an inclination α<90°relative to the equatorial plane, e.g. between 60° and 90°.

Advantageously, the first straight segment of the second transversegrooves has an extension smaller than 95% of the total extension of thesecond transverse grooves.

The extension and inclination of the first segment provide thecircumferential rib or the concerned block with a good flexibility,thereby providing the tyre with good brake/traction performances.

Conveniently, the second transverse grooves have a second, preferablystraight segment extending at most over 20% of the total extension ofthe second transverse grooves. Said second segment is preferablycounter-inclined relative to the first segment (i.e. it has an opposedinclination relative to the first segment).

Preferably, for each module of the tread pattern, the number of secondtransverse grooves in an area of the central portion facing the innerside of the tyre is greater than the number of second transverse groovesin an area of the central portion facing the outer side of the tyre.

Advantageously, the central portion can have at least two secondcircumferential grooves.

Preferably, the central portion can have three circumferential ribs,each comprising a plurality of blocks circumferentially defined by thesecond transverse grooves.

Alternatively, the central portion can have two circumferential ribscomprising a plurality of blocks circumferentially defined by the secondtransverse grooves and a circumferential rib comprising a plurality ofsecond transverse grooves having an axial extension smaller than 80% ofthe width of the circumferential rib itself.

In this embodiment, the circumferential rib comprising the plurality ofsecond transverse grooves having an extension smaller than 80% of thewidth of the circumferential row, is preferably located closer to thesecond shoulder portion of the tyre, i.e. the one facing the inner sideof the tyre, with respect to the rest of the ribs.

Advantageously, the second transverse grooves can be located at adistance of between 25 mm and 80 mm in circumferential direction.Preferably, in at least one circumferential rib of the central portion,the second transverse grooves are located at a distance of between 40 mmand 80 mm in circumferential direction.

Conveniently, the distance between the second transverse grooves in thecircumferential rib of the central portion closest to the inner side ofthe tyre is smaller than the distance between the second transversegrooves of the rib of the central portion closest to the outer side ofthe tyre.

Advantageously, each circumferential rib of the central portion has itsown void-to-rubber ratio. Preferably, said void-to-rubber ratio isgreater in the rib closest to the second shoulder portion.

Conveniently, the second circumferential grooves have a width greaterthan 12 mm.

Preferably, the first and/or the second circumferential grooves have amaximum depth greater than 5 mm.

Advantageously, the first and/or second circumferential ribs have alarge right section having a substantially trapezoidal or rectangularshape.

The first circumferential grooves comprise a first circumferentialgroove facing the outer side of the tyre and a first circumferentialgroove facing the inner side of the tyre, the first circumferentialgroove facing the outer side of the tyre having a width smaller than thewidth of the first circumferential groove facing the inner side of thetyre, thereby increasing the structural stiffness and resisting thestrong lateral forces.

Preferably, the tread has a third groove located on the first shoulderportion.

Advantageously, the third circumferential groove can have a widthsmaller than 4 mm.

Advantageously, the third circumferential groove can have a depthsmaller than 4 mm.

More characteristics and advantages of the invention will be nowillustrated referring to the embodiments shown by way of non-limitingexample in the accompanying figures, in which:

FIG. 1 is a schematic view of a footprint area of a tyre (in particulara rear tyre) mounted on a sport car having a suspension system with ahigh camber angle;

FIG. 2 is a perspective view of a tyre having a tread made according toan example of the invention;

FIG. 3 is an enlarged sectional view of the tread of FIG. 2;

FIG. 4 is a plan view of the tyre tread of FIG. 2;

FIG. 5 is a plan view of a modification of the tread of FIG. 2;

FIG. 6 is a plan view of a further modification of the tread of FIG. 2;and

FIG. 7 is a plan view of a further modification of the tread of FIG. 2.

In FIGS. 2-7, a tyre 1 having a tread 2 according to the presentinvention is shown.

The tyre 1 has a conventional structure and comprises a carcass, a treadband placed at the crown of the carcass, a pair of axially oppositesidewalls ending in beads reinforced with bead cores and respective beadfillers. The tyre preferably also comprises a belt structure interposedbetween the carcass and the tread band. The carcass is reinforced by oneor more carcass plies anchored to the bead cores, whereas the beltstructure comprises two radially and mutually overlapped belt strips.The belt strips are formed by parts of rubberized fabric encasing metalcords, parallel to each other in each strip and crossing those of theadjacent strips, preferably symmetrically inclined with respect to theequatorial plane. Preferably, the belt structure also comprises a thirdbelt layer, which is placed in a radially outermost position andprovided with cords substantially parallel to the equatorial plane.

The tyre 1 preferably has a H/C ratio, between the height of the rightsection and the maximum width of the section, of between 0.25 and 0.65.The nominal width of the section of the tyre 1 is preferably betweenabout 195 mm and 365 mm. The rim diameter of the tyre 1 is preferablybetween 16 and 22 inches.

To ensure not only a long mileage but also high performances during thewhole tyre life, especially as regards the driveability, the tread 2 hasa comprehensively small void-to-rubber ratio, i.e. smaller than 0.35,preferably smaller than 0.32.

The tread 2 is provided with circumferential grooves 3, 4, 5, 6,extending in a longitudinal direction.

The tread 2 comprises a central portion L1, a first shoulder portion L2located on the outer side of the tyre and a second shoulder portion L3located on the inner side of the tyre.

First circumferential grooves 3 and 6, respectively, axially delimit thefirst shoulder portion L2 and the second shoulder portion L3 withrespect to the central portion L1 of the tread 2.

Each first shoulder portion L2 and second shoulder portion L3 comprisesfirst transverse grooves 56, 66, respectively.

The respective transverse grooves 56, 66 are circumferentially repeated.

The first transverse grooves 56, 66 have a width greater than or equalto about 4 mm. Preferably, the first transverse grooves 56, 66 have awidth smaller than about 10 mm. For example, they can have a widthbetween about 4 and about 8 mm.

The centerline of the respective first transverse grooves 56, 66 istransverse or slightly inclined with respect to the axial direction.

In particular, the centerline of the grooves 56 forms, with theequatorial plane X-X, an angle to having an absolute value of between45° and 90°.

Preferably, the angle co is greater than 70°.

Preferably, each first transverse groove 56, 66 has a not-constantdepth, preferably gradually decreasing towards the axially externaledges of the tyre.

Each first transverse groove 56, 66 has a maximum depth at least equalto about 3 mm and smaller than about 10 mm. Preferably, each firsttransverse groove 56, 66 has a maximum depth of between about 4 mm andabout 8 mm.

The first transverse grooves 56, 66 have a first end locatedsubstantially at the respective axially external edge of the tread 2 andextend from such an end in a substantially axial direction over at least50% of the width of the shoulder portion in which they are located. Inthis way, the first transverse grooves 56, 66 significantly change thestiffness of the tread portions in which they are obtained, therebyaffecting the overall stiffness of the shoulder portions.

In the embodiments shown in FIGS. 4 and 5, the first transverse grooves56 located in the first shoulder portion L2 extend up to the firstcircumferential groove 3 and open out therein, whereas in theembodiments shown in FIGS. 6 and 7, an end of the first transversegrooves 56 located in the first shoulder portion L2 is far from thefirst circumferential groove 3.

An end of the first transverse grooves 66 located in the second shoulderportion L3 can be far from the first circumferential groove 6 such as,for example, in the embodiment shown in FIG. 7. Conversely, in theembodiments shown in FIGS. 4, 5, 6, the first transverse grooves 66 arejoined to the first circumferential groove 6 by means of sipes 23 havinga maximum width smaller than 2 mm, preferably smaller than 1 mm.

The sipes 23 are preferably counter-inclined with respect to the firsttransverse grooves 66.

Each sipe 23 has a preferably small axial extension, preferably lessthan 20% of the width of the second shoulder portion L3.

Each sipe 23 may have a substantially constant depth along itsextension, preferably a maximum depth smaller than 5 mm, more preferablysmaller than 3 mm.

According to an aspect of the present invention, the number of firsttransverse grooves 56 of the first shoulder portion L2 is smaller thanthe number of the first transverse grooves 66 of the second shoulderportion L3. With reference to the embodiment shown in FIGS. 4-7, foreach module of the tread pattern the number of first transverse grooves66 of the first shoulder portion L3 is about twice the number of firsttransverse grooves 56 of the second shoulder portion L2. The ratiobetween the number of grooves 66 located in the first shoulder portionL3 and the number of grooves 56 located in the second shoulder portionL2 can obviously be slightly different from the exact value of two: forexample by having 70 grooves located in the second shoulder portion L3,30-40 grooves can be provided in the first portion of the shoulder.

In the embodiments shown in FIGS. 4-7, the first shoulder portion L2also has a plurality of third transverse grooves 33.

The third transverse grooves 33 have a small depth (i.e. smaller than3-4 mm) and a short axial extension (equal to or smaller than about30-40%). Furthermore, they are located in the axially outermost part ofthe first shoulder portion L2, basically at the edge of the tread. Inthis way, the stiffness of the first shoulder portion L2 is notsignificantly affected by the third transverse grooves 33.

In the embodiments shown in the FIGS. 4, 6 e 7, the first shoulderportion L2 further has a plurality of fourth transverse grooves 34extending over less than 20% of the width of the first shoulder portionL2.

The fourth transverse grooves 34 may extend from the firstcircumferential groove 3 and/or may be located on the extendedcenterline of the second transverse grooves 16, which will be describedbelow.

The fourth transverse groove 34 can have a width smaller than about 3mm, preferably smaller than about 2 mm.

In the embodiments shown in FIGS. 4-7, the first shoulder portion L2also has a third circumferential groove 7. Such third circumferentialgroove 7 has a width smaller than 4 mm and a maximum depth smaller than4 mm.

The first and the second shoulder portions L2, L3 have a smallvoid-to-rubber ratio, in order to limit the mobility of the shoulderportions of the tyre tread.

Preferably, the first shoulder portion L2 and/or the second shoulderportion L3 have a void-to rubber ratio smaller than about 0.15,preferably smaller than about 0.10. Preferably, the first shoulderportion L2 and/or the second shoulder portion L3 have a void-to rubberratio greater than 0.05, preferably greater than 0.06.

In the embodiments shown in FIGS. 4-6, the central portion L has twosecond circumferential grooves 4, 5 so as to form three circumferentialribs 9, 10 e 11 whereas in the embodiment shown in FIG. 7 the centralportion L has only one circumferential groove 5 so as to form twocircumferential ribs 10 e 11.

In detail, in the embodiments shown in FIGS. 4-6, a firstcircumferential rib 9 is between the first circumferential groove 3 andthe second circumferential groove 4. A second circumferential rib 10 isbetween the second circumferential grooves 4 and 5. A thirdcircumferential rib 11 is between the second circumferential groove 5and the first circumferential groove 6.

The first shoulder portion L2 is separated from the first rib 9 by thefirst circumferential groove 3, whereas the second shoulder portion L3is separated from the third rib 11 by the first circumferential groove6.

Conversely, in the embodiment shown in FIG. 7, a first circumferentialrib 10 is between the first circumferential groove 3 and the secondcircumferential groove 5. A second circumferential rib 11 is between thesecond circumferential groove 5 and the first circumferential groove 6.

The first shoulder portion L2 is separated from the first rib 10 by thefirst circumferential groove 3, whereas the second shoulder portion L3is separated from the second rib 11 by the first circumferential groove6.

The first and/or second circumferential grooves 3, 4, 5, 6 may have awidth between about 5 mm and about 16 mm.

In greater detail, in the embodiments shown in FIGS. 4-6, the firstcircumferential groove 3 separating the central portion L1 from thefirst shoulder portion L2 has a width smaller than the width of thefirst circumferential groove 6 separating the central portion L1 fromthe second shoulder portion L3.

For example, the first circumferential groove 3 located towards theouter side of the tyre may have a width smaller than about 10 mm,preferably smaller than about 8 mm; the first circumferential groove 6located towards the inner side of the tyre may have a width smaller thanabout 15 mm, preferably smaller than about 14 mm.

On the contrary, in the embodiment shown in FIG. 7, the firstcircumferential groove 3 separating the central portion L1 from thefirst shoulder portion L2 has a width greater than the width of thefirst circumferential groove 6 separating the central portion L1 fromthe second shoulder portion L3.

For example, according to this embodiment, the first circumferentialgroove 3 located towards the outer side of the tyre may have a widthsmaller than about 15 mm, preferably smaller than about 14 mm; the firstcircumferential groove 6 located towards the inner side of the tyre mayhave a width smaller than about 13 mm, preferably smaller than about 12mm.

In all embodiments, the second circumferential grooves 4, 5 located inthe central portion L1 have a width greater than the width of the firstcircumferential grooves 3, 6 located so as to separate the centralportion L from the shoulder portions L2, L3. For example, the secondcircumferential grooves 4, 5 may have a width greater than about 12 mm.

The first and/or second circumferential grooves 3, 4, 5, 6 preferablyhave a maximum depth ranging from about 4 mm to about 11 mm, morepreferably from about 5 mm to about 8 mm.

The second circumferential grooves 4, 5 and the first circumferentialgroove 6 can have a substantially constant width throughout their depth,in order to provide excellent drainage performances.

In other words, their groove bottom can be wide enough, comparable tothe width of the groove as measured at the radially outermost surfacesof the adjacent blocks, and the inclination of their lateral walls withrespect to the groove centerline can be small.

In detail, in the embodiments shown in FIGS. 4-6, the secondcircumferential grooves 4, 5 and the first circumferential groove 6 areformed so as to have a large right section having a substantiallytrapezoidal, preferably nearly rectangular, shape.

The first circumferential groove 3 located towards the outer side of thevehicle has a width gradually decreasing in a radial direction towardsthe groove bottom.

In other words, the right section of the first circumferential groove 3tapers towards the groove bottom.

The first circumferential groove 3 has a width smaller than 8 mm,preferably greater than 5 mm, more preferably equal to 6 mm. The lateralwall facing the outer side of the first circumferential groove 3 has aninclination of about 15° relative to its centerline axis, whereas theopposed lateral wall can have an inclination of about 5° relative to thecenterline axis.

The first circumferential groove 6 located towards the inner side of thetyre has a right section greater than the right section of the firstcircumferential groove 3 located towards the outer side of the tyre.Preferably, the second circumferential groove 5 located towards theinner side of the tyre has a right section greater than the rightsection of the second circumferential groove 4 located towards the outerside of the tyre, and the latter has a right section greater than theright section of the first circumferential groove 6 located towards theinner side of the tyre.

Conversely, in the embodiment shown in FIG. 7, the secondcircumferential groove 5 and the first circumferential grooves 3, 6 areformed so as to have a right section of large size, having asubstantially trapezoidal shape, preferably almost rectangular.

Preferably, the second circumferential groove 5 located towards theinner side of the tyre has a right section greater than the rightsection of the first circumferential groove 6 located towards the innerside of the tyre.

In the embodiments shown in FIGS. 4-7, the central portion L comprisescircumferential ribs characterized by low void-to-rubber ratios, inorder to increase the “rubber/ground interface” at the central portionL1 thereby achieving excellent handling performances, low noise, lowrolling resistance and wear evenness.

At least one circumferential groove 9, 10, 11 (preferably each of them)has a void-to-rubber ratio smaller than about 0.06, more preferablysmaller than about 0.05.

In the central portion L1, the tread 2 shown in FIGS. 4-6 has avoid-to-rubber ratio, without considering the first and secondcircumferential grooves 3, 4, 5, 6, smaller than about 0.06, preferablysmaller than about 0.05.

In fact, in the central portion L1 the water is primarily, or almostentirely, drained by means of the circumferential grooves 3, 4, 5, 6,which have, as previously described, a width and/or depth properly sizedfor this purpose.

The circumferential ribs 9, 10, 11 comprise second circumferentialgrooves 16, 17, 18 extending, at least in one of the circumferentialribs 9, 10, 11, over at least 40%, preferably 80% of the width of thecircumferential row.

The second transverse grooves 16, 17, 18 have a width smaller than orequal to about 3 mm, preferably smaller than about 2 mm.

The second transverse grooves 16, 17, 18 preferably have a maximum depthgreater than 4 mm, preferably smaller than 10 mm, still more preferablysmaller than 8 mm.

The second transverse grooves 16, 17, 18 are located at a distance in acircumferential direction preferably between 25 mm and 80 mm in thecircumferential direction. Preferably, in at least one of thecircumferential ribs 9, 10, 11, the distance is between 40 mm and 80 mm.

The embodiments shown in FIGS. 4-6, as previously disclosed, arecharacterized by a central portion L1 comprising three circumferentialribs 9, 10, 11.

In the embodiments shown in FIGS. 4-6, the distance d between the secondtransverse grooves 16, 17 located in the circumferential ribs 9, 10 isgreater than the distance between the second transverse grooves 18located in the circumferential rib 11 closest to the inner side of thetyre.

In this embodiment shown in FIGS. 4 and 6, the second transverse grooves16, 17, 18, extend over the whole width of the circumferential ribs 9,10, 1 i such that blocks are defined on all the ribs 9, 10, 11.

In this embodiment, for each rib 9, 10, 11, the second transversegrooves 16, 17, 18 define a plurality of blocks, 13, 14, 15,respectively.

In the embodiment shown in FIG. 5, the second transverse grooves 16, 17extend over the whole width of the ribs thereby defining blocks 13, 14only in the first and the second circumferential ribs 9, 10. On thecontrary, the second transverse grooves 18 are not extended over thewhole width of the third circumferential rib 11 adjacent to the secondshoulder portion L3.

In the embodiment shown in FIGS. 4-6, each block 13 of the firstcircumferential rib 9 is axially delimited by two segments 103 and 104of circumferential grooves and circumferentially delimited by two secondtransverse grooves 16.

Each second transverse groove 16 has a centerline provided with at leastone first straight segment 107 and one second straight segment 106.

The second straight segment 106 has a length substantially smaller thanthe length of the first segment 107. The first straight segment 107preferably has an extension greater than 50%, and preferably smallerthan 95% of the total extension of the second transverse grooves 16. Thesecond segment 106 instead has an extension smaller than 20% of thetotal extension of the second transverse grooves 16.

The first segment 107 preferably has an inclination α≥45°, morepreferably α≥60°, relative to the equatorial plane X-X.

Advantageously, the first segment 107 preferably has an inclinationα<90° relative to the equatorial plane X-X.

In the embodiment shown in figure, the second straight segment 106 iscounter-inclined relative to the first segment 107.

The second transverse grooves 16 extend so as to be parallel to eachother at least along a portion thereof. Preferably, they aresubstantially parallel to each other along their whole extension.

Preferably, the second transverse grooves 16 of the firstcircumferential rib 9 have a not-constant depth but a stepped profile.In other words, as shown in FIG. 3, they exhibit a central area havingthe maximum depth and located in the middle of the first circumferentialrib 9 and two portions 38 having smaller depths and located axiallyexternal with respect to the central one. The two portions 38 withsmaller depths have a short axial extension and are located next to thecircumferential grooves 3 and 4.

Such stepped profile of the grooves 16 provides stiffness to the block13 at its ridges, thereby preventing or anyway reducing the occurrenceof uneven wear.

Each block 14 formed in the second rib 10 is axially delimited by twosegments 204 and 205 of circumferential grooves and circumferentiallydelimited by two second transverse grooves 17.

Preferably, the blocks 14 formed in the groove 10 are slightly staggeredin a circumferential direction with respect to the blocks 13 of thecircumferential row 9.

Each second transverse groove 17 of the circumferential rib 10 has acenterline provided with at least one first straight segment 107, asecond straight segment 106 and a third straight segment 108. The secondstraight segment 106 and the third straight segment 108 substantiallyhave the same length.

The second straight segment 106 and the third straight segment 108 havea length substantially smaller than the length of the first segment 107.The first straight segment 107 preferably has an extension greater than50%, and preferably smaller than 95% of the total extension of thesecond transverse grooves 17.

The first segment 107 preferably has an inclination σ>45°, morepreferably α≥60°, relative to the equatorial plane X-X.

Advantageously, the first segment 107 preferably has an inclinationα<90° relative to the equatorial plane X-X.

The second segment 106 and the third segment 108 have instead anextension smaller than 20% of the total extension of the secondtransverse grooves 17.

The second segment 106 is located at an end of the first segment 107 andthe third segment 108 is located at the axially opposed end of the firstsegment 107.

In the embodiment shown in FIGS. 4-6, the second straight segment 106 iscounter-inclined with respect to the first segment 107 and also thethird segment 108 is counter-inclined with respect to the first segment107.

Furthermore, the first straight segment 107 of the second transversegrooves of the second circumferential rib 10 is counter-inclined withrespect to the first straight segment 107 of the second transversegrooves 16 of the first circumferential rib 9.

In the embodiment shown in FIGS. 4-6, the second circumferential grooves17 of the second circumferential rib 10 are positioned so that thedistance d between each other is substantially equal to the distancebetween the second transverse grooves 16 of the first circumferentialrib 9.

The second transverse grooves 17 are substantially parallel one anotherat least along a portion thereof. Preferably, they are substantiallyparallel one another along their whole extension.

Preferably, the second transverse grooves 17 of the secondcircumferential rib 10 have a not-constant depth but a stepped profile.In other words, as shown in FIG. 3, they exhibit a central area havingthe maximum depth and located in the middle of the secondcircumferential rib 10 and two portions 48 having smaller depths andlocated axially external with respect to the central one. The twoportions 48 with smaller depths have a short axial extension and arelocated next to the circumferential grooves 4 and 5.

Such stepped profile of the second transverse grooves 17 providesstiffness to the block 14 at one of its ridges so as to prevent oranyway reduce the occurrence of uneven wear.

Referring to the embodiments of FIGS. 4 and 6, each block 15 of thethird circumferential rib 11 is axially delimited by two segments of thecircumferential grooves 305 and 306 and circumferentially delimited bytwo second transverse grooves 18.

Still referring to the embodiments shown in FIGS. 4 and 6, each secondtransverse groove 18 of the third circumferential rib 11 has acenterline provided with at least one first straight segment 107 and onesecond straight segment 106.

The second straight segment 106 has a length substantially smaller thanthe length of the first segment 107. The first straight segment 107preferably has an extension greater than 50%, and preferably smallerthan 95% of the total extension of the second transverse grooves 18.

The first segment 107 preferably has an inclination α≥45° morepreferably α≥60°, relative to the equatorial plane X-X.

Advantageously, the first segment 107 preferably has an inclinationα<90° relative to the equatorial plane X-X.

The second segment 106 has an extension smaller than 20% of the totalextension of the second transverse grooves 18.

In the embodiment shown in FIGS. 4 and 6, the second straight segment106 is counter-inclined relative to the first segment 107.

In the embodiment shown in FIGS. 4 and 6, the first segment 107 of thesecond transverse grooves 18 of the third circumferential rib 11 iscounter-inclined with respect to the first segment 107 of the secondtransverse ribs 17 of the second circumferential rib 10.

On the contrary, the first segment 107 of the second transverse grooves18 of the third circumferential rib 11 has a concordant inclination withrespect to the first segment 107 of the second transverse grooves 16 ofthe first circumferential rib 9.

The centerlines of second transverse grooves 18 are parallel one anotherat least along a portion thereof. Preferably, they are substantiallyparallel one another along their whole extension.

In the embodiment shown in FIGS. 4 and 6, the second transverse grooves18 of the third circumferential rib 11 are positioned so as to have adistance d/2 between each other with respect to the distance between thetransverse grooves 16 of the circumferential rib 9.

Preferably, the second transverse grooves 18 of the thirdcircumferential rib 11 have a not constant depth but a stepped profile.In other words, as shown in FIG. 3, they exhibit a central area havingthe maximum depth and located in the middle of the third circumferentialrib 11 and two portions 58 having smaller depths and located axiallyexternal with respect to the central one. The two portions 58 withsmaller depths have a short axial extension and are located next to thecircumferential grooves 5 and 6.

Such stepped profile of the second transverse grooves 18 providesstiffness to the block 15 at one of its ridges so as to prevent oranyway reduce the occurrence of uneven wear.

In the embodiments shown in FIGS. 4-6, the outer ridge 45 of the firstcircumferential rib 9, facing the first shoulder portion L2, is rounded.Such characteristic works against uneven wear of the axially externalridge 45 of the first circumferential rib 9.

Similarly, also the outer ridge 46 of the circumferential rib 10, facingthe first shoulder portion L2, is rounded.

The tread shown in FIG. 5 is a modification of the one in FIGS. 4 and 6and similar parts are referred to by the same numerals. The tread 2 ofFIG. 5 is completely similar to the tread 2 of FIGS. 4 and 6 except forthe third circumferential rib 11 and, in particular, the secondtransverse grooves 18 obtained therein.

In this embodiment, the second transverse grooves 18 do not extend overthe whole width of the third circumferential row 11, but over less than80%, preferably about 50-60%, of the width of the third circumferentialrib 11.

More particularly, the second transverse grooves 18 may extend from thecircumferential groove itself up to about 50-60% of the width of thethird circumferential rib 11. Preferably, they alternately extend in acircumferential direction from circumferential grooves 5, 6 that areaxially opposite to the third circumferential rib 11.

In other words, in the circumferential direction if a second transversegroove 18 extends from the second circumferential groove 5 up to about50% of the width of the third circumferential rib 11, the secondtransverse groove 18 that is circumferentially consecutive extends fromthe first circumferential groove 6, and then the alternation iscircumferentially repeated.

Such a choice provides the third circumferential rib 11 with a greaterstiffness, by decreasing the void-to-rubber ratio thereof.

FIG. 6 shows a tread 2 which is a modification of the one in FIG. 4wherein similar parts are referred to by the same numerals. The tread ofFIG. 6 is in every way similar to the tread of FIG. 4 except for theshape of the second grooves 16 of the first circumferential rib 9 andfor the first shoulder portion L2.

In this embodiment, the width of the second transverse grooves 16 of thefirst circumferential rib 9 is not-constant over their whole extension,but is greater in a first portion 68 thereof.

Preferably, at least one surface portion of the first portion 68 has awidth greater than 2 mm, more preferably smaller than 5 mm.

Preferably, the first portion 68 of the second grooves 16 is notextended over the whole width of the circumferential row 9. In theembodiment of FIG. 6, it only extends over about 50% of the width of thefirst circumferential rib 9.

Also the fourth transverse grooves 34 at least in one surface portionthereof, located in the first shoulder portion L2, have a width greaterthan 2 mm, preferably smaller than 5 mm.

In addition, as previously disclosed, in the embodiment shown in FIG. 6,one end of the first transverse grooves 56 located in the first shoulderportion L2 is apart from the first circumferential groove 3.

The embodiment shown in FIG. 7, as previously mentioned, comprises twocircumferential ribs 10, 11 in the central portion L1.

Preferably, the second transverse grooves 17, 18 are not extended overthe whole width of the circumferential ribs 10, 11.

Preferably, according to this embodiment, the second transverse grooves17, 18 extend at most over 80%, preferably at most 60%, of the width ofthe circumferential rib in which they are located.

The second transverse grooves 17 of the first circumferential rib 10extend from the circumferential groove 5 towards the equatorial planeX-X.

Each second transverse groove 17 of the first circumferential rib 10 hasa centerline having preferably an inclination α≥45°, more preferablyα≥60°, relative to the equatorial plane X-X.

Advantageously, the centerline of the second transverse groove 17 of thecircumferential rib 10 has an inclination α<90° relative to theequatorial plane X-X.

According to this embodiment, the second circumferential grooves 17 ofthe first circumferential rib 10 are positioned so as to havesubstantially the same distance d from each other.

The second transverse grooves 17 are substantially parallel one anotherat least along a portion thereof. Preferably, the second transversegrooves 17 are substantially parallel one another along their wholeextension.

Preferably, the second transverse grooves 17 of the firstcircumferential rib 10 have a not-constant depth but a stepped profile.In other words, they comprise a central area having the maximum depthand located in the middle of the first circumferential rib 10 and oneportion having smaller depth and located axially external with respectto the central one. The portion with smaller depth has a short axialextension and is located close to the first circumferential groove 5.

Still according to this embodiment, the first circumferential rib 10 hasa plurality of fifth transverse grooves 35 having an extension smallerthan 35% of the width of the first circumferential rib 10.

The fifth transverse grooves 35 may extend from the firstcircumferential groove 5 and are alternately arranged with respect tothe second transverse grooves 17 without intersecting the latter.

Preferably, the fifth transverse grooves 35 extend parallel to thesecond transverse grooves 17.

The fifth transverse groove 35 can have a maximum width smaller thanabout 3 mm, preferably smaller than about 2 mm.

The fifth transverse grooves 35 can substantially have a distance dbetween each other.

Still according to this embodiment, the second circumferential grooves18 of the second circumferential rib 11 are positioned so as to havesubstantially the same distance d/2 from each other.

Furthermore, according to this embodiment, the second transverse grooves18 of the second circumferential rib 1 are not parallel butcounter-inclined with respect to each other.

In detail, each second transverse groove 18 is counter-inclined withrespect to the second transverse groove adjacent in a circumferentialdirection.

Moreover, still according to this embodiment, each second transversegroove 18 extends from a circumferential groove 5 or 6.

Advantageously, the centerline of the second transverse groove 18 of thefirst circumferential rib 10 has an inclination α≥45°, more preferablyα≥60°, relative to the equatorial plane X-X.

Preferably, the outer ridge 54 of the first circumferential rib 10facing the first shoulder portion L2 is rounded. Such characteristicworks against uneven wear of the outer ridge 54 itself.

Another embodiment, not shown in figures, comprises a central portion L1in every way similar to the central portion L1 of FIG. 7, but comprisingan additional circumferential rib, substantially without transversegrooves, located between the first circumferential groove 3 and thecircumferential rib 10.

According to different embodiments of the invention, different samplesof the tyre have been made, in particular having the tread of FIG. 6(invention 1) and having the tread of FIGS. 4-5 (invention 2).

Different sets of tyres were subjected to comparison tests with somesets of equally sized PZero™ tyres manufactured by the Applicant.

Various sport cars used in the tests were first equipped with four tyresof the invention and then with four comparison tyres.

Straight stretch and cornering aquaplane tests, braking tests on dry andwet road surfaces, drive behavior tests on dry and wet road surfaces,noise tests inside and outside the car and comfort tests, have beencarried out.

The straight stretch aquaplane test has been carried out on a straightstretch of smooth asphalt having a predetermined length (100 m) coveredwith a water layer having a predetermined constant height (7 mm)automatically restored any time the tested car went past. During thetest, the vehicle goes into the water layer at a predetermined speed(about 70 Km/h) in total grip conditions, and accelerates until itcompletely loses grip.

The cornering aquaplane test has been carried out on a track stretch ofsmooth and dry asphalt at a bend of constant radius (100 m) having apredetermined length and comprising, in a final stretch, an area ofpredetermined length (20 m) flooded with a water layer having apredetermined thickness (6 mm). The test has been carried out atconstant speed, with different speeds.

During the test, the maximum centrifugal acceleration and the maximumspeed of the car when the total aquaplane occurs, are detected.

The braking test is performed both under wet and dry road conditionswith tyres equipping a vehicle provided with an antilock braking system(ABS) of the wheels.

This braking test was carried out on a straight stretch of asphalt, bothunder dry and wet conditions, and the stopping distance at apredetermined starting speed, typically 100 km/h under dry conditionsand 80 Km/h under wet conditions, has been detected.

The travelling behavior test, under dry and wet surface conditions, iscarried out on predetermined tracks, typically tracks closed to traffic.By simulating some characteristic manoeuvres (such as lane changing,overtaking, slalom between cones, entering and exiting a corner) at aconstant speed as well as while accelerating and decelerating, the testdriver evaluates the performances of the tyre by giving the latter anumerical appraisal during the above mentioned manoeuvres.

The comfort evaluation was appraised considering the sensations the testdriver perceived as regards the tyre ability to absorb the roughness ofthe road surface.

The subjective noise test has been carried out at decreasing speeds from120 Km/h (or a speed compatible with the power and streamlined noise thecar emits, anyway not less than 100 Km/h) to 0 Km/h with the gearshiftin neutral, the engine and the air-conditioning unit off (if possible)and the windows closed.

The loudness (sound level and frequency as a speed function) of thetread blocks has been evaluated. The best tyre minimizes all thedescribed sound components when the speed changes.

The homologation noise test is carried out on predetermined outsidetracks by positioning two microphones spaced one from another such thatthe vehicle can pass between them. In order to perform each measurement,the vehicle has to travel a predetermined stretch in a straight line topass between the two microphones so as to have the longitudinalmid-plane of the vehicle as close as possible to the straight linepassing through the centerline of the distance between the twomicrophones.

The driver has to put into neutral gear and turn the engine off beforethe front part of the vehicle intersects the line joining the twomicrophones. Values of the testing speed can change according to thetype of tyre, being generally between 70 and 90 Km/h.

The test results are shown in Table I wherein ratings are in percentagevalues and values referring to the comparison tyre are set to 100.

TABLE I Comparison Invention 1 Invention 2 Aquaplane during cornering100 110 108 Aquaplane in straight stretch 100 106 110 Subjective noise100 102 106 Homologation noise 100 110 110 ABS braking on dry surface100 110 105 ABS braking on wet surface 100 105 104 Behavior on drysurface 100 105 110 Behavior on wet surface 100 100 102 Comfort 100 101100

In Table I, values greater than 100 show an improvement with respect tothe comparison tyre.

The test results show that the tyre of the invention has a generallybetter behavior.

The Applicant believes that such a result, in particular in regard tothe behavior tests, at least partly owes to the tread pattern accordingto the invention, since it allows the footprint area to deform verygradually and progressively. For example, during cornering with suddenload transfer with vehicles provided with suspensions having a highcamber angle, especially at the rear tyres, the Applicant believes thatthe tread pattern allows to achieve a shape of the footprint area at themost substantially mirrored with respect to the one shown in FIG. 1,i.e. longer on the outer side of the tyre and tapered on the inner sidethereof but without total loss of grip.

1. A car tyre having a tread comprising a central portion located acrossan equatorial plane, a first shoulder portion located towards an outerside of the tyre and a second shoulder portion located towards an innerside of the tyre, the central portion being separated from said shoulderportions by two first circumferential grooves having a respectiveminimum width of about 5 mm, wherein: said first shoulder portion andsaid second shoulder portion comprise a plurality of first transversegrooves having a first end located substantially at a respective edge ofthe tread, having a width greater than or equal to about 4 mm and anaxial extension equal to at least 50% of the width of the shoulderportion in which they are located; said two first circumferentialgrooves are a first circumferential groove facing towards the outer sideof the tyre and a first circumferential groove facing towards the innerside of the tyre, the first circumferential groove facing towards theouter side of the tyre having a width smaller than the width of thefirst circumferential groove facing towards the inner side of the tyre;the number of said first transverse grooves of the first shoulderportion is lower than the number of said first transverse grooves of thesecond shoulder portion; said central portion comprises at least onecircumferential rib, comprising a plurality of second transversegrooves; and said second transverse grooves have a maximum width smallerthan or equal to about 3 mm and define in said at least onecircumferential rib a void-to-rubber ratio smaller than 0.06; secondtransverse grooves comprise a first substantially straight segmentextending over at least 50% of the total extension of the secondtransverse grooves, said first substantially straight segment having anextension smaller than 95% of the total extension of the secondtransverse grooves.
 2. The tyre according to claim 1, wherein said treadcomprises a module which is cyclically repeated along thecircumferential development of the tyre, and wherein for each module ofthe tread the number of first transverse grooves of the second shoulderportion is about twice the number of first transverse grooves of thefirst shoulder portion.
 3. The tyre according to claim 1, wherein saidfirst substantially straight segment having an inclination α>45°relative to the equatorial plane.
 4. The tyre according to claim 1,wherein said second transverse grooves comprise a second substantiallystraight segment extending at most over 20% of the total extension ofthe second transverse grooves, said second substantially straightsegment being counter-inclined relative to the first segment.
 5. Thetyre according to claim 1, wherein said central portion has at least twosecond circumferential grooves.
 6. The tyre according to claim 5,wherein central portion has three circumferential ribs comprisingrespective pluralities of blocks circumferentially defined by the secondtransverse grooves.
 7. The tyre according to claim 5, wherein saidcentral portion has two circumferential ribs comprising respectivepluralities of blocks circumferentially defined by the second transversegrooves, and a third circumferential rib comprising a plurality ofsecond transverse grooves having an axial extension smaller than 80% ofthe width of the circumferential rib.
 8. The tyre according to claim 1,wherein said central portion comprises a second circumferential grooveand two circumferential ribs.
 9. The tyre according to claim 7, whereinsaid second transverse grooves extend at most over 80% of the width ofthe circumferential rib in which they are located.
 10. The tyreaccording to claim 7, wherein in each circumferential rib, the secondtransverse grooves are located at a spacing of between 25 mm and 80 mmin circumferential direction.
 11. The tyre according to claim 10,wherein one said spacing in the rib of the central portion closest tothe inner side of the tyre is smaller than another said spacing in therib of the central portion closest to the outer side of the tyre. 12.The tyre according to claim 7, wherein each circumferential rib of thecentral portion has a set void-to-rubber ratio, said void-to-rubberratio being greatest for a rib closest to the inner side of the tyre.13. The tyre according to claim 5, wherein said second circumferentialgrooves have a width greater than 12 mm.
 14. The tyre according to claim5, wherein said first and/or second circumferential grooves have amaximum depth greater than 5 mm.
 15. The tyre according to claim 1,further comprising a third circumferential groove located on the firstshoulder portion, the third circumferential groove having a widthsmaller than the width of the first circumferential groove facingtowards the outer side of the tyre.
 16. The tyre according to claim 15,wherein said third circumferential groove has a width smaller than 4 mm.17. The tyre according to claim 15, wherein said third circumferentialgroove has a maximum depth smaller than 4 mm.
 18. The tyre according toclaim 1, wherein the plurality of first transverse grooves of the firstshoulder portion have a second end that reaches the firstcircumferential groove facing towards the outer side of the tyre. 19.The tyre according to claim 15, wherein the plurality of firsttransverse grooves of the first shoulder portion traverse the thirdcircumferential groove.